It has been described that among Japanese males one in twenty (approximately 5%) are color deficient observers, while among white males one in twelve (approximately 8%) are color deficient observers. Color deficient observers are color deficient due to any of three cone photoreceptor cells existing in color normal observers being abnormal or defective. A case of a defective red cone photoreceptor cell is called a “protan deficiency,” a case of a defective green cone photoreceptor cell is called a “deutan deficiency,” and a case of a defective blue cone photoreceptor cell is called a “tritan deficiency.”
Among these, the tritan deficiency is at a low frequency, which is one person per several million people, and therefore, the term “color deficient” typically means the protan deficiency and the deutan deficiency.
Because the protanopes and the deuteranopes have similar sensitivity curves in the red cone photoreceptor cell and green cone photoreceptor cell, color appearances and color combinations (combination colors) difficult to differentiate between them are very similar. It has been described that it is difficult for the protanopes and the deuteranopes to sense a difference between the colors in a combination of red and green.
Today, a variety of innovations are taken toward color schemes with the aim of enhancing information in various types of print materials, notices, electronic images, and the like in one's immediate surroundings. However, even if it is easy for a color normal observer to recognize information because it is easy to distinguish colors in its color scheme, it is difficult for a color deficient observer to distinguish the colors in the color scheme, and therefore, it is difficult to recognize the information, which leads to a barrier (interference) of information recognition in many cases.
In order to solve this problem, there have been proposed color deficient corrective (correcting) glasses, color improvement/modification means, and the like in Patent Documents 1, 2, and 3.
Methods such as these glasses and means aim to improve the distinction between the colors by correcting transmitted colors with respect to a specific color combination in which it is difficult for a color deficient observer to sense a difference between its colors.
As such, any of these methods controls only the transmittance in a wavelength band with the maximum sensitivity of the three types of cone photoreceptor cells, but does not control the entire visible light wavelength band.
Therefore, those methods have a certain effect on a color combination in which it is difficult for a color deficient observer to distinguish its colors. However, because the control for a transparent wavelength band is imperfect, it is difficult to achieve an effect on other color combinations in some cases.
Further, in these methods, a transmitted light is colored, and for example, it appears reddish overall in some cases. As a result, in many cases, an observer has a sense of discomfort, and feels fatigued in his/her daily life.
Additionally, in recent years, demand for barrier-free designs, and further, a universal design have grown in strength on a worldwide basis. For example, in public facilities, various efforts such as installations of elevators and stair lifts, low-floor buses, toilets for wheelchairs, automobiles and telephone boxes for the disabled have been made.
That is, the concept of a universal design is not to cure or reverse disabilities of the disabled (persons with disabilities), but is intended to consider the possibility that both the physically sound and the disabled live without distinction from the point in time of facility and building design.
Therefore, it is necessary to understand what circumstances cause inconvenience for the disabled.
However, in the present situation, the response to a universal design (barrier-free) for color deficient observers is much less advanced than the response to other disabled. It has been described that a major cause thereof is that it is difficult for color normal observers to intuitively understand the inconveniences which color deficient observers sense.
In response to such a problem, as an effort to give consideration to color deficient observers, in recent years, a method for reproducing colors which color deficient observers sense by color simulation software has been used in some municipalities and the like. That is, a color normal observer experiences a color world which a color deficient observer views in a simulated manner, and an attempt has been made to apply the experience to color designs for public print materials and the like such as disaster prevention hazard maps (refer to Patent Document 4).
In such an image processing method by software, it is necessary to input image data into a personal computer or the like, and to scan and detect a color combination in which it is difficult for a color deficient observer to distinguish its colors by use of a dedicated image processing program. Accordingly, the method is effective for an image formed by a data processing device such as a personal computer, data necessarily input into the data processing device, and the like.
However, in such an image processing method by software, for notices/facilities/public indications which are already installed, industrial products, and the like, because it is necessary to once input image data into a data processing device, and to scan and detect it, there are many working processes, which makes it difficult to import the method into an everyday workflow.
Further, because it is necessary for such an image processing method by software to depend on a method for observing an image on a computer display, resultingly, an entire visual field does not approach to a color world which a color deficient observer senses, and it can only be said that the method is insufficient for an actual sensation of inconveniences. As a greater problem, there is the problem that it is necessary to determine an object in advance, and to take a photograph thereof, and the like, which is inconsistent with real-time performance, and this is far from physically sensing inconveniences in one's daily life.    Patent Document 1: Japanese Published Patent Application No. H06-18819 A    Patent Document 2: Japanese Published Patent Application No. H09-313521 A    Patent Document 3: Japanese Translation of International Application (Kohyo) No. H09-503402 A    Patent Document 4: Japanese Published Patent Application No. 2005-167543 A